The invention relates to an apparatus for screwing together parts with little strength, in particular an apparatus for joining shells, molds, foundry cores, preferably bottom cores and water-jacketed cores, as well as a corresponding method.
The joining of parts with little strength is always a problem, since a complicated handling or a costly transportation of such parts to a screwing station can lead already to a breakage of these parts. To avoid a breakage of the parts to be joined, it is also necessary to provide for both a fine feed and a slight tightening torque of the screw.
Cores as are employed in the foundry practice, are such parts with little strength, so that the problems arising in the practice will be described below with reference to such cores.
In the foundry practice, cores are formed by hand or with the aid of core molding machines in special, multipart core boxes or core dies. In general, the cores are manufactured by blowing, plugging and shooting. The individual cores are assembled or joined in separate operations by bonding or nailing. As a result, the method of manufacture is very complicated, labor-intensive and time-consuming (German Patent DE 35 26 265 and German Utility Model GM 75 15 919).
Further it has been found in practice when joining parts with little strength or when assembling individual cores by nailing or screwing that the material of the parts to be joined breaks easily as a result of shearing forces which occur in this process.